The embodiments described herein relate generally to a detection technique for chemical substances, and, more particularly, to using additives to detect contraband substances such as explosives, narcotics, pesticides, and chemical warfare agents by means of spectrometry.
Certain contraband substances—such as ammonium nitrate (AN), ammonium nitrate fuel oil (ANFO) and urea nitrate (UN)—can be difficult to detect through discharge type sources such as, for example, atmospheric pressure chemical ionization (APCI) because the discharge of air generates abundant atmospheric NO3− ions that can overlap with the nitrate NO3− ion signal from ANFO and UN (as well as other explosives). Known techniques have tried to differentiate the two signal contributions, but the sensitivity is compromised by the background atmospheric NO3− signal. Other techniques that are known attempt to bind additives to explosives for detecting chemical substances; however, these techniques are unable to differentiate between NO3− ions from the air and nitrate NO3− ions from explosives.
In many known substance detection techniques, adduct ions are commonly used. Adducts are products of combining two or more distinct molecules to form a single reaction product containing all of the atoms of all of the component molecules, thereby forming a distinct molecular species. Such distinct molecules may be positive or negative ions and the associated adduct ions are formed in either a positive ion mode or a negative ion mode, respectively, to enhance the sensitivity of spectrometry devices for certain classes of compounds of interest. The use of adducts facilitates ionization through ion attachment to only slightly ionizable or completely non-ionizable substances. Also, the use of adducts facilitates ionization through stabilizing fragile molecular ions which otherwise would fall apart during analysis thereby producing multiple fragments of substances of interest that may decrease the sensitivity to their detection.
The known techniques, however, use additives to bind with the parent molecules of explosives to create an adduct. The present disclosure has overcome the deficiencies of the prior art by shifting the signal of a sample of a substance of interest by complexing and reacting the sample with additives that react less efficiently with background signals and bind a dissociated ion portion of the sample to create an adduct that allows for identification of the sample of the substance of interest.